Rates of dementia and Alzheimer?s disease are 40-100% higher in African-Americans versus non-Hispanic whites, and African-Americans (AA) ? one of the fastest-growing segments of the elderly population in the US - - will comprise the largest segment of the ?silver tsunami? of dementia if trends persist. Understanding cognitive aging in elderly AA represents an urgent public health need. Though cognitive decline and dementia are major health issues for older AA individuals, this is a heterogeneous group and understanding how differences in exposures and health over the lifecourse influence variability in latelife cognition is critical for developing interventions and understanding how to reduce risk. Population-based cohort studies of cognitive ageing in AA are few, specifically those which follow trajectories of cognitive aging in the 5th and 6th decade of life. AA have higher rates of stroke, diabetes and hypertension, established risk factors for Alzheimer?s disease, and have broader exposure to adverse life experience which may impact late-life cognitive health. The 2013 NIH State of the Science on Preventing Cognitive Decline recommended a lifecourse approach, incorporating early life exposures with brain aging in late life. Yet, while increased vulnerability to Alzheimer?s disease and vascular disease make AA a crucial group to identify lifecourse exposures, most of what is known about early life risk and protective factors of Alzheimer?s disease and cognitive aging is largely from populations based studies of non-Hispanic whites. We propose a lifecourse study of brain aging that will utilize 5 decades of prospectively collected life history and health data. Our goals are: 1).Characterize heterogeneity in longitudinal change in domain specific cognition in a representative population based cohort of well characterized African- Americans, 2). Examine cumulative exposure to vascular risk, psychosocial factors and early life experience over 50 years and evaluate effects on cognitive aging, and 3). Evaluate structural MRI imaging markers of brain status on domain-specific cognitive function and explore brain status as mediators of the association between lifecourse factors and cognition. Findings will directly benefit a population that is at highest risk of Alzheimer?s disease and dementia in the United States, has been understudied from a lifecourse perspective, and is expected to more than double in size by 2030 within the age 65+ segment of the US population.